Directional boring, commonly called horizontal directional drilling, is a steerable trenchless method of installing underground pipes, conduits and cables or the like in a shallow arc, along a prescribed subsurface bore path by using a specialized drilling rig. The drilling assembly that creates the boring is surface launched at a shallow angle and is steered along the predetermined path.
Pipes laid, or well casing installed in this manner can be made of materials such as iron, steel, PVC, polyethylene, polypropylene, or the like.
Products installed by directional drilling are typically used for utilities transmission or distribution, water supply, or remediation of contaminated soil or groundwater.
With this type of drilling there is typically minimal impact on the surrounding area compared to trenching or other alternatives. Directional boring can often be used when trenching or excavating is not practical, such as under roadways, or other existing structures. It is suitable for a variety of soil and rock conditions.
One feature of horizontal directional drilling is the incorporation of electronic locating equipment that enables the driller or another crew member to determine the relative position of the drill head in three dimensions and in real time. This information—typically X and Y coordinates along the ground surface, the depth below ground surface, and the current pitch or angle of the drill bit—is used to determine if the bore is being advanced along the desired path and to enable the driller to make steering corrections as necessary to maintain the path.
Electronic locating equipment may be supplied in several forms and uses several different technologies. The simplest, easiest to employ, and least expensive locating equipment is battery powered and comprises a combination of an instrument package that is placed in a housing behind the drill bit (the “sonde” and “sonde housing”) and a receiver assembly (the “receiver”) that is carried by a technician at the ground surface along the bore path, over the drill bit, during drilling operations. The sonde contains sensors to monitor various parameters such as temperature, tool pitch and roll, and battery strength, as well as a radio transmitter and antenna that emits an electromagnetic signal that is analyzed by the receiver to calculate the drill head position. This combination of sonde and receiver is known in the industry as a “walkover locating system.”
The exemplary walkover sonde that is commonly used in the industry comprises a metallic and resin cylinder that contains a circuit board, transmitting antenna, and battery compartment. The circuit board contains various sub-components, including the RF transmitter, antenna, and other sensors described above. The electronics and other components on the circuit board are encapsulated in an epoxy resin to provide a singular electronics package that is water-resistant and durable.
In another embodiment of a locating sonde for deeper drilling, the sonde contains geomagnetic sensors that detect the earth's magnetic field for determination of tool azimuth. These systems made be used at depths too great to receive a signal at the surface from a subsurface transmitter. Through computer analysis of azimuth, pitch, and drill string length calculations, the sonde position may be fixed in three dimensions. In this embodiment, the sonde does not contain an antenna to transmit a signal directly to the ground surface, but instead sends the signal through a hard-wired wireline connection which is threaded through the drill string to a connection at the drill rig itself. The wireline is used for signal transmission as well as to supply power to the sonde.
Due to practical engineering constraints in smaller drilling equipment, locating sondes have been limited in size, both in diameter and length, in order to fit into common drill tooling. For bores up to approximately 80 feet in depth, the currently available sondes provide adequate signal strength for locating. However, below this depth, signal strength typically declines to an unusable level. Further, the existing sonde packaging does not permit the use of larger antennae or additional batteries to emit a more powerful signal. To date, there has not been integration between the sonde itself and the housing which encloses it in order to provide this enhanced capability.
The capabilities of this technology are evolving, and borings of greater depth and length are now feasible that were not possible previously. As a result, there is an increased need for locating equipment that has enhanced capabilities to enable locating at greater depths and longer bore lengths, and that also have longer battery life to allow greater distances to be drilled before battery failure. A locating system that allows increased battery capacity or a larger antenna array would be of benefit to the industry.
Additional developments in the industry include the use of miniaturized radio repeaters that can be embedded in the individual drill rods comprising a drill string. Such repeaters may be used to transmit a radio signal for great lengths up the interior of the drill string, which serves as a wave guide to focus the transmission. Such a system could be easily adapted to use with locating technologies intended for depths greater than typically used for battery operated sondes. Such a system would eliminate the requirement for a wireline to transmit the sonde signal to the surface, but with current technology would not eliminate the need for the wireline to supply power to the sonde.